WO 2016/102187 A1 discloses a rotary screen printing press having a first and a second screen cylinder, which form two print positions with an impression cylinder. Between the first and second print positions a radiation dryer is provided, directed toward the lateral surface of the impression cylinder. A squeegee located inside the screen printing cylinder can be engaged from the inside against the screen printing forme and disengaged from said printing forme by means of a drive, mechanically independently of the rotation of screen cylinder and impression cylinder.
DE 10 2015 208919 A1 discloses a screen printing unit having a screen cylinder that can be thrown onto and off of an impression cylinder, and a squeegee inside the screen cylinder that can be set against the screen and moved away therefrom.
EP 1582349 A1 discloses a method for printing by the screen printing method onto sheets conveyed by a chain conveyor, in which upon entering the print position, the gripper drawing the sheet is received by a channel on the circumferential surface by an impression cylinder, and is then positioned at the trailing end of the channel by the relative speed between chain conveyor and impression cylinder. During said positioning, squeegee and screen cylinder preferably remain thrown off of the impression cylinder. During this phase, squeegee and screen cylinder begin to move into the position required for printing. For printing, the screen cylinder is brought in contact with the impression cylinder and the squeegee is brought in contact with the screen.
The object of EP 3210777 A1 is to reduce waste sheets by printing onto even the first sheet of a production run. In conventional processes, in contrast, the squeegee is not placed in an engaged position until the thrown-on screen cylinder has completed a full revolution.
When the screen printing cylinder is thrown off, a lack of ink removal along with possible rotation may result in an undesirable build-up of ink on the outer surface of the screen, and when thick layers come into contact with the impression cylinder surface or during printing of the first sheets, this can ultimately lead to undesirable soiling of the impression cylinder. This effect is particularly adverse when an intermediate drying step is carried out by means of a dryer directed toward the lateral surface of the cylinder. This leads rapidly to a build-up of ink. During intermediate drying, in particular, the dried ink becomes hard, forming peaks, and can cause damage to the screen printing forme. Printing ink that is hardened in this way is very difficult to remove from the cylinder surface.